The several researchers. One main argument comes

The study of mentalrepresentations is a central concern in the overall theory of cognition and themind. Concepts are mental representations of entities arising from ourexperiences, and are fundamental for prediction and communication. Our mentalorganization influences how we use our knowledge, and these models ofcategorizations have been developed and studied through the past decades.

Traditionalcategorization models emphasized heavily on feature-based similarity whilerecent evidences have shown categorization to be include more than justcomparisons. Contemporary approaches such as Wisniewski & Bassok’s (1999)and Lin & Murphy’s re-evaluate the role of thematic relations, suggestingthe importance of thematic relations, together with taxonomic relations, inmental organization. In this paper, we will first discuss the shift of researchlooking at thematic relations, and then tie in current research on adult use ofthematic relations with Funnell’s (2001) Levels of Meaning model.

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Similarity grounding categorizationSimilarityunderpins many traditional models of the organization in categorization. Oneclassic model is the prototype approach, in which the categorical membership ofthe novel object is determined by comparing the object to the prototype thatrepresents the category (Rosch & Mervis, 1975). The other is the exemplarapproach, where the comparison is made between the novel object and the actual categoricalexemplars (Brooks, 1978, 1987). While stark differences exist between the twomodels, both models hinge on similarity between the novel object andcategories’ representation for categorization purposes. Similarityhad been argued against as insufficient for grounding categorization by severalresearchers.

One main argument comes from Goodman (1972), claiming thatsimilarity is too flexible to ground categorization. Specifically, Goodmanargued that similarity is not based on solely perceptual input, but involvesother factors. Goodman’s strong claim has been supported by empirical evidencesshowing that other factors like expertise (Sjoberg, 1972) and environment(Hardnad, 1978) influence similarity judgments as well. In response, Goldstone(1994) suggested that similarity is indeed an integration of multiple sourcesof information.  Tversky’s Contrast Model(1977), for instance, proposes that similarity between two entities increasesas they share more features, and decreases as they possess more distinctivefeatures. However, Goodman argued that the features entered into comparison canbe very broad and any substantial changes in features can affect similarityjudgment, rendering similarity a slippery slope. Nevertheless, Goldstone’s(1994) paper attempted to find a mediating ground between similarity andcategorization, suggesting that though similarity may be slippery, it is still applicableto most categories and is necessary in helping us understand the notion ofcategorization, thus meriting a reassessment of its role.  THESTUDY OF THEMATIC RELATIONSNeed for Dual-Process Model Theconventional view of conceptual organization heavily emphasized on the notionof similarities, with category representing a set of entities sharing anessential core of similar features, whether perceptual, functional orbiological (Medin & Ortony, 1989).

This relation is referred to as the taxonomic relation (e.g. cow-horse; pen-pencil). Taxonomic relation is alsothe core of the classic prototype and exemplar models mentioned above. However,over the recent decades, a growing body of evidence has shown that thematicrelations are as important as taxonomic relations in categorization. Thematic relations are complementaryrelations among entities that co-occur together in space and time (Markman,1981, 1989). These relations can be spatial (e.g.

a lid is on top of acontainer), functional (e.g. a comb is used to brush hair), temporal (e.g. dryingclothes after washing them) and/or causal (e.g. a lighter produces fire).BeforeWisniewski & Bassok’s (1999) paper, cognitive research had based similarityon a single process model involving only feature comparisons.

However,Wisniewski & Bassok’s paper served as a major turning point, when the needof a dual-process model involving comparison and integration as well as theeffects of stimulus compatibility was highlighted. Their paper was motivated byunexpected finding in Bassok & Medin’s (1997) study. Their study startedout with the premise that comparison was the only process involved insimilarity judgment.

Surprisingly, they found that when actions were taxonomicallyunrelated and therefore less alignable, participants tended to thematicallyintegrate them into a joint theme or scenario. This then led to Wisniewski& Bassok designing experiments to predict the stimulus compatibilityeffects on similarity judgment. Insteadof statements describing actions, object pairs were intentionally designed tovary orthogonally in terms of alignability and thematic relatedness, resultingin four types of base-target object pairs. The target was either high (+) orlow (-) on thematic relatedness (T) and on alignability (A), in relation to thebase object in the pair.

For example, one quintuplet of base-target objectsused is chair-table (A+T+), chair-bed (A+T-), chair-carpenter (A-T+) andchair-electrician (A-T-). Participants rated object pairs on a 7-pointsimilarity scale and were required to write down an explanation for theirratings. Highly alignable pairs were rated as more similar  than poorly alignable pairs. Object pairs withpreexisting thematic relations were also scored higher similarity ratings thanpairs without thematic relations.

Participants’ explanations were divided intoinstances of comparison and integration. Participants tended to compare objectpairs that were highly alignable and without preexisting thematic relations;while participants tended to integrate object pairs that were poorly alignableand with preexisting thematic relations. The robustness of the stimuluscompatibility effect was further examined in Studies 2 & 3. Despite thetask instructions modified to emphasize the appropriateness of comparison (inStudy 2) and integration (in Study 3), participants’ responses were stillstrongly affected by the stimulus compatibility. Theold processing model which involves only comparison cannot account for theabove findings. Wisniewski & Bassok’s paper thus demonstrated the need to extendto a dual-process model and consider not just taxonomic relations (whichinvokes comparison), but thematic relations (which invokes integration) whichmay be equally important in similarity judgment as well. Adults’ Use of Thematic RelationsInthe next decade, an increasing bulk of research were devoted into studyingthematic relations in mental representations. Previous developmental literaturein the 1960s and 1970s generated extensive work on thematic relations but only inchildren’s conceptual development, but not in older children or young adults.

Inhelder & Piaget (1964) found that when children were tasked to sort toys,children under 5 primarily categorized based on objects that “belongedtogether” which they then tell a story about. These developmental studies ledto the conclusion of a thematic-to-taxonomic shift as part of children’sconceptual development. However, recent literature suggested otherwise, arguingthat thematic relations do not fade away as children’s concept develop, but arestill present in adults’ concepts. For example, Smiley & Brown (1979)’sstudy found the majority of educated elderly participants preferring to use thematicover taxonomic relations.

Other literatures also found elderly preferring touse thematic relations as compared to younger adults (Smiley & Brown, 1979;Annet, 1959; Denney, 1974). Education factor also entered into the study asLuria (1979) and Sharp et al (1979) found evidence that uneducated adults usedmore thematic relations. Motivated by these literatures, Lin & Murphy(2001) attempted to investigate the use of thematic relations in educated,adult participants. Lin& Murphy (2001) presented an intensive study on adult’s use of thematicrelations, extended across ten experiments, with each experiment debunking possiblecriticisms in the preceding.

Experiment 1 to 8 investigated thematiccategorizations in American adult college students while Experiment 9 & 10investigated the conceptual content of thematic groupings. Forced choice triadtask were used, in which participants decided which of the two matches (onetaxonomic, one thematic) goes best with the target to form a category. Experiment1 & 2 found that young, educated adults tended to use thematiccategorization 62% and 49% of the time respectively.

The task procedures inExperiment 3 to 5 differed slightlty (e.g. presenting stimuli in words insteadof word-picture combination) in attempt to replicate Smiley & Brown’s(1979). Smiley & Brown previously found that 75% of their college student participantsusing taxonomic categories 84% of the time. However, up till Experiment 5, Lin& Murphy still found very different results from Smiley & Brown, whichcould be attributed to two-third of Smiley & Brown’s original stimuli notpublished. Nevertheless, Lin & Murphy found convincing evidence of adultreadily using meaningful thematic relations in categorization. The second partof the study provide noteworthy evidence of the utility of thematic relations,specifically that thematic relations can guide category-based induction, justlike taxonomic relations.

Overall, Lin & Murphy’s experiments sum up tosuggest that the importance of thematic relations in adults’ concepts, more thanprevious research have typically concluded. TAXONOMICAND THEMATIC RELATIONSLevels of Meaning ModelHavingdemonstrated the importance of thematic relations in addition to taxonomicrelations in categorization, we will now introduce Funnell’s (2001) Level ofMeaning Model to bring the two ideas together. Unlike Tulving’s (1972) classicdistinction between semantic and episodic memory, Funnell’s model represents meaningon a continuum which connects both semantic and episodic characteristics. Funnelldiscussed recent evidence from semantic dementia patients whose memory ofobjects and words meanings is preserved only for current and personal use. PatientEP, reported by Funnell (1996), was a woman who had severe semantic memorydeficits. Although she was unable to identify objects in confrontational tasks(e.

g. word-picture matching) when in clinic, her husband reported her usingsimilar objects appropriately in daily activities back at home. Classic modelsof conceptual representation in semantic memory, which focused only on theencyclopaedic nature of context-free information, could not account for theobservation. Studies of semantic dementia patients thus revealed theinvolvement of scripts in semantic memory. With this, Funnel developed an extended semantic memory model, wheremeaning is represented on a continuum, from being entirely embedded in thephysical context of personal experience, to being entirely stripped ofcontextual information. This continuum is continuously sustained and modifiedby new learning from our current personal experiences. Contextual informationof current information are stored as a specific physical script of a specificscene at the level of “Specific Event Knowledge”. This includes informationregarding the specific objects and role players involved, organized around aspecific goal (e.

g. preparing a cup of Nescafé coffee this morning). As thesame physical scenes are experienced frequently and centered on same goal,physical properties specific to the particular scene (e.g. red coffee mug, bluecoffee mug) are replaced by more general properties (e.g. description of atypical mug).

This more abstracted level of the event script is known as “GeneralEvent Knowledge”. Finally, the most abstracted level – “Concepts” – isrepresented independently, free from typical contextual information and areavailable for use in novel context. Concepts can vary in specificity, fromsubordinate (e.g. coffee mug) to basic (e.g.

mugs) to superordinate (e.g.cutleries) levels. This model accounts for the observation in semantic dementiapatients.

As semantic memory breaks down, the context-free concepts arecompromised, and patients can no longer recognized objects presented out ofcontext. However, their less abstract general event knowledge allow them tostill use and recognize objects within the context of a familiar physicalscript. Funnell’s(2001) model is relevant to the research of thematic and taxonomic relations incategorization as it connects the two into a single model.

Concepts relate totraditional taxonomic theories which organizes information based on similarproperties, while General Event Knowledge relate to thematic theories whichorganizes information based on the co-occurrence in event or theme. This modelthus provides further support for people (which includes adults) making use ofboth taxonomic and thematic similarity, since thematic relations underlies thebasic learning mechanism of meaning at the event knowledge level, which is thendeveloped through further abstraction into taxonomic concepts. Individual Differences inTaxonomic-Thematic TendenciesAnotherissue that surfaced often in the study of taxonomic-thematic relations was theindividual differences in the strength of taxonomic vs thematic relations. Forinstance, in Lin & Murphy’s (2011) study, participants were classified intopredominantly taxonomic or predominantly thematic based on their responses. InSchwaryz et al.’s (2011) study of picture-naming errors, individuals withaphasia were found to differ in their tendencies to produce taxonomic andthematic errors. However, prior to Mirman & Graziano’s (2011) paper, theextent of such individual differences were neither investigated nor establishedfor neurologically intact adults. Before the 21st century, moststudies investigating thematic relations have used tasks that explicitly requiredassessing the two types of relations (e.

g. the “triad” task). Few studieslooked at tasks where thematic relations are not required. Mirman thus investigated the activation of taxonomic and thematic relationseven when task demands do not require them.

The inclusion of such tasks isimportant in the establishment of real individual differences in the strengthof taxonomic vs thematic relations, as genuine individual differences should bestable across different types of tasks, whether or not the task demands requireassessing taxonomic or thematic relations.Inthe first part of the study, participants were presented a four-image displaycontaining a target object, a semantic competitor (taxonomic or thematic) andtwo unrelated distractors. Participants heard a spoken word, and wereinstructed to either click or look at the corresponding image. Eye movements weretracked and analyzed. Participants were found to more likely fixate on thesemantically related competitors than the unrelated distractors in bothtaxonomically and thematically related conditions. A relative measure was thencomputed to represent each individual’s tendency to activate taxonomicrelations more strongly than thematic relations.

This computation was then usedin the second part of the study to predict the individual’s tendency to choosetaxonomic over thematic options in a triad task. The number of taxonomicchoices in the triad tasks were found to positively associate with theindividual participants’ relative taxonomic competition effect size computedfrom the spoken-word task. Thus, the cross-task relation suggested that thetendency to activate taxonomic vs thematic relations was indeed due toindividual differences, rather than being specific to task or stimulus.CONCLUSIONOverthe years, the study of mental organization have evolved, from the oldsingle-process model to the contemporary dual-process model which includes bothcomparison and integration, as suggested by Wisniewski & Bassok (1997). Thestudy of thematic relations previously understood to be present only inchildren’s conceptual development, is now thought to also be present in adults’concepts (Lin & Murphy, 2011). The interdependence of taxonomic andthematic relations is then tied in with Funnell’s Levels of Meaning model. Individualdifferences in tendency to use taxonomic or thematic are evident, supported byMirmna & Graziano’s (2011) cross-task evidence. These recent evidences arecritical in the study of mental representation, because categorization isfundamental to how we use our knowledge – to identify, predict and communicate.

Thus, deepening the understanding of how our mind organizes information willbenefit a wide range of studies in cognitive research and beyond. 


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